Two-temperature refrigerating system



Sept 20, 1949. E. w. ZEARFOSS, JR 2,432,569

TWO-TEMPERATURE REFRIGERATING SYSTEM 2 Sheets-Sheet 1 Filed Feb. 28,1945 INVENTOR. EM 7/f&wfiw

BY hbwmwiw Filed Feb. 28, 1945 Sept. 20, 1949. w, E F JR 2,482,569

' TWO-TEMPERATURE REFRIGERATING SYSTEM 2 Sheets-Sheet 2 INVENTOR. m 71Zawyr: J

Patented Sept- 20, 1949 TWO-TEDIPERATURE REFRIGERATING SYSTEM Elmer W.Zeal-loss, In, Philadelphia, Pa assi or, by mesne assignments, to PhilcoCol-pomtion, Philadelphia, Pa., a corporation of PennsylvaniaApplication February 28, 1945, Serial No. 580,108

12 Claims.

The present invention relates to refrigeration and particularly tomulti-temperature refrigerating systems. More especially, the inventionis concerned with so-called two-temperature refrigerating systems andspecifically pertains to an improved method and arrangement forobtaining two different refrigerating temperatures with a systemincluding a single compressor and two separate evaporatorswhich arerespectively adapted to maintain two separate zones or isolatedcompartments at the different temperatures.

It is common knowledge in the art that, if an evaporator is capable ofhandling its refrigeration load, the'temperature of the associatedrefrigerated zone or compartment will depend largely on the amount ofevaporating refrigerant present within the evaporator and on theevaporating pressure. Therefore, if two or more evaporators included inone and the same system, are caused to operate at different pressuresand are provided with an adequate supply of refrigerant, separate zonesor isolated compartments with which the said evaporators arerespectively associated may be effectively refrigerated and kept atdifferent temperatures;

In the so-called two-temperature system ineluding a, single compressorand two separate evaporators (generally referred to as the lowtemperature evaporator and the high temperature evaporator,respectively), it has been proposed to utilize automatic temperature orpressure responsive means for controlling the flow of refrigerantthrough the system inzficordance with rises, beyond pre-set limits, inthe temperature or pressure of either or both of said evaporators. vHowever, in such automatically controlled two-temperature system, oneevaporator is given absolute preference over the other evaporator withthe result that should the evaporator which has preference be under anunusually heavy load, the other evaporator may, in effect, be shut downfor possibly dangerously long periods of time, because then the flow ofrefrigerant through the latter will be interrupted until the preferredevaporator is fully satisfied.

Attempts have been made to rectify this objectionable result by usingeither solenoid or pressure actuated valve mechanism controlled throughtemperature responsive means, such mechanisms functioning to transferrefrigerant from the evaporator which under normal conditions haspreference, to the other evaporator when the temperature of the latterrises to an abnormally high value.

The use of refrigeration control mechanisms of the kind abovementioned,.not only complicates the system, but moreover introduces anumber of critically related devices which in themselves are of acomplicated nature, so that the proper function of the system no longerdepends upon simple conditions within the system itself but must relyupon the accurate operation of each and every one of such devices.

It is an object of this invention to provide a system which is capableof afiording two differcnt refrigerating temperatures with two separateevaporators in circuit with a single compression chamber, and which iscapable of keeping each evaporator within its desired temperature rangewithout giving undue preference to either evaporator and without usingcomplicated arrange ments of intricate control devices.

It is also an object of the invention to provide a refrigerating systemincluding two separate evaporators in circuit with a single compressionchamber wherein the evaporators are operated respectively at differenttemperatures by controlling the fiow of refrigerant directly inaccordance with predetermined departures from an established state ofbalance between the suction pressure of one evaporator and the suctionpressure of the other evaporator.

Another object of the invention is to provide a refrigerating systemincluding a relatively low temperature evaporator and a relatively hightemperature evaporator in circuit with a single compression chamberwherein said evaporators are maintained withintheir respective selectedtemperature ranges directly by conditions within the system itself.

Another object of the invention is to provide a two-temperaturerefrigerating system employing two evaporators operating at differentpressures together with associated means for establishing an artificialbalance between the evaporator pressures, said means being responsive todepartures from. said established pressure balance and operating tomaintain the evaporators at their respective pressures and to therebymaintain the desired temperature range at which each evaporator is tofunction.

Still another and more specific object of the invention is to provideimproved control means for a refrigerating system employing a pluralityof evaporators adapted for operation at different suction pressures torefrigerate separate zones or isolated compartments at differenttemperatures, said control meansfunctioning to establish a balancebetween such suction pressures and being acted upon directly bypredetermined de- 2 partures from such established balance resulting bytend to maintain a definite temperature difference between theevaporators.

Other objects and advantages of the invention will appear from thefollowing description based upon the accompanying drawings in which:

Fig. 1 is a transverse vertical sectional view of a hermeticmotor-compressor unit and control device incorporating the features ofthe invention and illustrating One embodiment of the improvedtwo-temperature refrigeration system;

Fig. 2 is a semi-diagrammatic representation showing a slightly modifiedembodiment of the system.

As illustrated in the drawings, the refrigerating system contains atleast two evaporators 5 and 6 respectively disposed within separatezones or isolated compartments 1 and 8 which are to be refrigerated andmaintained at different temperatures.

The evaporators 5 and 6 are in circuit with a condensing unit whichincludes a motor-compressor 9 and a condenser In. The motor-compressor 9is of the type having a single compression chamber I l which is definedby a cylinder 12 and is provided with the usual reciprocating piston l3,intake port 14 and exhaust, port I5. The condenser I II is connected, inthe customary manner, for instance by means of a conduit IT, with aliquid receiver tank l8 adapted for the storage of condensedrefrigerant. Liquid refrigerant from the tank I8 is supplied to theevaporators 5 and 6 through liquid line l9, refrigerant flow regulators20 and 2|, such as expansion or other suitable valves, beingrespectively associated with the evaporators to control the admission ofliquid refrigerant therein. Refrigerant evaporated in the evaporators 5and 5 is withdrawn. therefrom through suction lines 22 and 23respectively, at the proper rate to maintain the desired suctionpressure within each evaporator.

In the arrangements shown in the drawings, the evaporator 5 is to coolits associated zone or compartment 1 at temperatures lower than those atwhich the evaporator 5 cools its associated zone or compartment 8.Therefore, in accordance with the accepted practice in the art, theevaporator 5 may be called the low temperature evaporator, and theevaporator 6 may be called the high temperature evaporator.

It is well understood in the art, that the ability of an evaporator tocool a zone or compartment to a certain temperature, is determinedprimarily by the suction pressure maintained in the evaporator and thatthe lower the suction pressure, the lower the temperature at which azone or compartment may be cooled by the evaporator. Accordingly, if theevaporators 5 and 6 contained in the system shown in the drawings, areto cool their respective zones or compartments 1 and 8. to differenttemperatures, it is imperative that said evaporators be maintained atdifferent suction pressures.

In accordance with the present invention, this is accomplished bycontrolling the communication between the evaporators 5 and 6 and thecompression chamber ll, directly as a result of predetermined departuresin an established condition of balance between the pressures in the twoevaporators. With this mode of control, it is possible to maintain acontinuous differential Within a given range between the pressures inthe two evaporators so that, during operation of the system, andalthough both evaporators are in circuit with one and the samecompression chamber, the supply of refrigerant to either evaporator atthe expense .of the other can continue only to the limit of the saidrange at which point the flow of the refrigerant through the oneevaporator will be automatically interrupted and flow through the otherinitiated, this automatic periodic shift from one evaporator to theother continuing until both have been satisfied.

Control of the communication between the compression chamber and thesaid evaporators, is effectively accomplished by means of a singlepressure responsive device, designated generally by the referencecharacter 24 and included within the refrigerant circuit at a pointintermediate the compression chamber and the evaporators in the mannerto be presently described.

The system shown in Fig. 1 is capable of subjecting the evaporatedrefrigerant withdrawn from the low temperature evaporator to two-stagecompression so that said evaporator may be operated effectively within asub-zero temperature range. In this particular embodiment of theinvention the pressure responsive device 24 preferably takes the form ofa multiple valve mechanism comprising a valve casing 25 and a pair ofspaced interconnected valve members 26 and 27, respectively mounted foraxial movement within and longitudinal of said valve casing. Formedwithin the walls of the valve casing 25 and adapted to accommodate thevalve members 26 and 21, are relatively spaced co-axial recesses 28 and29 each having oppositely disposed valve seats 30 and 3|. In mountingthe valve members 26 and 21 in the manner stated, three distinctnoncommunicating spaces 32, 33 and 34 are provided within the valvecasing 25.

The respective valve members are adapted to seat selectively on thevalve seats 30 or 3|, and it is to be noted that said members seatsimultaneously on their respective valve seats 30 and simultaneouslyalso on their respective valve seats 3| For that purpose, the valvemembers 26 and 27, as shown, are preferably connected rigidly by meansof a rod 35 so that they move as a unit between the respective seats.

With reference to Fig. 1 of the drawings, it is pointed out that whenthe valve members 26 and 21 are seated on their respective seats 30 thatis in the lower position as shown in full lines, a casing port 36,connected with the suction line 22 of the low temperature evaporator 5,is in communication with a port 3! which is connected through a conduit38 with the intake port I4 of the compression chamber I I and a casingport 39, connected with a conduit 40 leading from the exhaust port l5.of said chamber II, is in communication with a port 4| which isconnected through a conduit 42 opening into a hermetically sealed space43. This space 43 is defined by a housing 44 which preferably is themotor-compressor housing into which also opens the suction line 23 ofthe high temperature evaporator 6. The opening of said suction line 23,however, is controlled by means of a suitable check valve 45 adapted toprevent the flow of gaseous refrigerant from the space 43 into saidevaporator 6.

Referring again to the showing of Fig. 1, it will be noted that when thevalve members 26 and 21 are seated on their respective seats 3|, thatis,

in the upper position as indicated in broken lines, the port 31 is incommunication with port 4|, and port 39 communicates with a port 46which is connected through a conduit 41 with the refrigerant condenserIll.

The system including the control valve device 24 is a closedcircuit, andit will be appreciated that a pressure difierential may be maintained onopposite sidesof the valve members 26 and 21. In this connection, it, ispointed out that, in practice, the relative size or surface area ratioof the valve members 26 and 21 is such that under the prevailingpressures only the larger member, which in the embodiment shown in Fig.1 is. the member 26 controlling the communication between port 31 andeither port 36 or port 4|, is capable of actuating the valve structure;the forces exerted by the smaller member, which in the embodiment shownis the member 21 controlling the communication between port 39 andeither port 4| or 46, being to all intents and purposes negligible.Because of this feature the valve member 26 may be termed the drivingvalve member.

In the circuit arrangement illustrated in Fig. 1, three distinctpressures are present, that is a high pressure which exists in the space32 below the valve member 21, in the condenser in, liquid receiver tank'|8and liquid line l'9 up to the regulators and 2|; a low pressure whichexists in the low temperature evaporator 5, suction line 22 and space 34above the valve member 26; and, an interstage pressure which exists inthe high temperature evaporator 6, suction line 23,- hermeticallysealed-space 43 and the space 33 between said valve members. a Low orinterstage pressure exists in the conduit 38, and interstage or highpressure exists in conduit 40, depending upon whether the valve membersare seated in lower or upper position. From the foregoing, it will beunderstood that, normally, a definite pressure diflerential exists onthe opposite sides of the driving valve member 26, the interstagepressure acting on the underside of the said valve member being greaterthan the low pressure acting on the upper side of said member.

In accordance with the present invention, these pressures are in effectequalized or balanced, and for that purpose suitable supplementalpressure developing means is provided, in the form in the presentinstance of a coil spring 49 arranged to act upon the upper side of thevalve member 26. The spring 49 is adapted to establish an artificialpressure balance between the two evaporator pressures and, for thatreason, the spring is so constructed that its pressure combined with thelow pressure at a desired minimum value on the upper side of the drivingvalve member 26, will balance the interstage pressure at a desiredminimum value on the underside of said valve member 26. Moreover, thespring 49 is constructed to have an exceedingly low "spring rate, sothat its pressure on the valve member is not materially changed bymovement of said valve member between its upper or lower positions.

Also, in accordance with the present invention, a means 59 is providedwhich is capable of resisting, within predetermined limits, a change inpressure on either the under side or the upper side of the driving valvemember, such means thus providing for a predetermined pressuredifferential at which the valve is to operate in controlling the flow ofrefrigerant through the system. As shown in Fig. 1, this pressureresisting means 60 may be in the form of spring pressed ball detents ofthe type represented at 6|, mounted for engagement with either the upperor lower side edge portion of the valve member 26 depending upon whethersaid member is in the lower or upper position. With a device of thissort, it will be apparent that the pressure on either side of the valvemember 26 must. vary from the aforedescribed' balance establishedbetween the evaporator pressures, to an extent suflicient to overcomethe resistance of such device before the valve can move from one to theother of its positions.

In order that the control devicev 24 and its mode of operation may bemore clearly understood, the following specific example is given:

Assuming that the system is charged with Freon-12" and it is desired tooperate the evaporator 5 at say 5 F. and the evaporator 6 at say +20 F.Then, according to published temperature-pressure measurement tables,the pressure in evaporator 5 should be approximately 7 lbs. per sq. in.gage, and the pressure in evaporator 6 should approximate 21 lbs. persq. in. gage. Thus a pressure differential of approximately 14 lbs.should exist between the two evaporators.

In accordance with the present invention, therefore, the spring 49 wouldbe constructed to develop a force equal to this 14 lbs. differential, sothat when the system is stabilized with the evaporator 5 at -5 F. andthe evaporator 6 at +20 F., the pressures on the opposite faces of thedriving valve member 26 tending to displace said member will bebalanced. It now becomes clear that by using supplemental pressuremeans, such as spring 49, on the low pressure side of said valve member26, slight variations from the balanced pressures due totemperature-pressure changes in either or both of the evaporators willbe reflected on the valve and will tend to actuate the same. The extentof departure from the balance of pressures which is required to actuatethe valve is determined by the pressure resisting means 56. Forinstance, if the spring pressed ball mechanisms 5i are constructed toresist unbalanced pressures of less than 2 lbs. upon the valve, thenmovement of the valve from one to the other of its positions will nottake place unless there exists a diiferential of at least 2 lbs. betweenthe pressures acting on the opposite sides of the valve member 26. Underthese conditions, in other words, when the valve is in the lowerposition, it will be moved to the upper position only if the pressurebelow the driving valve member 26 reaches a value of at least 2 lbs.more than the value of the pressure above said memher; and conversely,when the valve is in the upper position, it will be moved to the lowerposition only if the pressure above the driving valve member attains avalue of at least 2 lbs.

communication between the low temperature evaporator and the compressionchamber ll through suction line 22, valve space 34 and conduit 38, andthat movement of the valve into upper position establishes communicationbetween the high temperature evaporator 6 and said compressing chamberthrough suction line 23, hermetically sealed space 43, conduit 42, valvespace 33 and conduit 38. v

As hereinbefore stated, the system as illustrated in Fig. 1 is capableof producing two-stage compression in addition to maintaining theevaporators Sand 6 at different temperature-pressure values. This isaccomplished in the following manner:

Let it beassumed that at the initiation of or during an "on-cycle thecondition within the system is such that the interstage pressure withinthe high temperature evaporator 6 and therefore within the space 43, aswell as in the valve space 33, has been reduced to the desired minimumvalve, and that the pressure within the low temperature evaporator andconsequently in the valve space 34 has increased sufficiently tounbalance the pressure on the driving valve member 26 to an extent suchthat the valve is moved to the lower position, that is, to the positionshown in full lines. The flow of refrigerant then follows the courseindicated by the solid arrows in Fig. 1, that is, low pressure gaseousrefrigerant from the evaporator 5 is admitted to the compressing chamberII through the suction line 22, port 36, valve space 34, port 31,conduit 42 and inlet port l4, and is discharged at increased firststagepressure into the hermetically sealed space 43 through exhaust port l5,conduit 40, port 39, valve space 33, port 4| and conduit 42. Dischargeof gaseous refrigerant at increased first-stage pressure into thehermetically sealed space l3,

will of course raise the value of the interstage pressure in said space,but because of the check valve 45 which will close under the pressurerise, the flow of such gaseous refrigerant into the high temperatureevaporator is prevented so that the condition existing in saidevaporator is not affected.

Withdrawal of gaseous refrigerant from the low temperature evaporator 5reduces the pressure therein and therefore tends to maintain saidevaporator at its desired temperature. However continued pumping of therefrigerant at increased first-stage pressure into the hermeticallysealed space 43 causes the pressure therein to gradually increase untilit reaches a value sufficiently high to overcome the pressure on theupper side of the driving valve member 26, at which point the valve unitis caused to move to the upper position, that is, the position shown inbroken lines. When this occurs, the flow of refrigerant then follows thecourse indicated by the broken arrows, that is, gaseous refrigerant atinterstage pressure is permitted to flow into the compressing chamberIl' through conduit 42, port 4|, valve space 33, port 31, conduit 38 andintake port l4, and is discharged at condensin high or second-stagepressure into the condenser I8 through exhaust port l5, conduit 48, port39, valve space 32, port 45 and conduit 41. The high pressure gaseousrefrigerant gives up its heat in the condenser and condenses therein toreturn, in a liquified state, into the receiver tank l8 whence theliquid refrigerant is supplied to the evaporators 5 and 6 in properlymetered quantities through flow regulator 20 and 2|.

If at any time during second-stage operation I tinues until the pressureon the upper side of the driving valve member 28 attains a valuesufficient to again move the valve to the lower position therebyinitiating another first-stage operation. This repeated switching fromfirst-stage to second-stage operation and from second-stage tofirst-stage operation takes place until the sys-v tem becomes stabilizedwith both evaporators at the desired lowest temperature-pressure valuewhen the end of an on-cycle" is reached.

From the foregoing description, it will be understood that while thesystem operates to maintain the evaporators respectively at theirdesired temperature levels, it does so without unduly impeding theperformance of either evaporator since neither is completely shut downuntil the other is fully satisfied, but rather the evaporators arealternately subjected to refrigeration depending upon existingconditions within the system itself. Moreover because the system asshown in Fig. 1 is capable of producing two-stage compression, it ispossible to operate and maintain the low temperature evaporator attemperature ranges much lower than would otherwise be practical with acompressing unit of equal displacement.

If it is not necessary or desired to operate and maintain the lowtemperature evaporators within such low temperature ranges, theembodiment of the system diagrammatically shown in Fig. 2 may be used.For all intents and purposes, this embodiment is substantially the samein con struction and operation as that shown in Fig. 1, with theexception that it does not include the two-stage compression feature andtherefore the pressure responsive device 24 is constructed and arrangedin the refrigerant circuit to control only the flow from the evaporators5 and 6 to the compression chamber II and not to control lilac flow fromsaid chamber to the condenser With particular reference to Fig. 2, itwill be noted that the pressure responsive device 24 comprises a valvemechanism including a valve casing 25a and a valve member 2612. Thisvalve member is mounted for axial movement within and longitudinally ofsaid valve casing which, for that purpose, is provided with a recess 21adefined by a pair of oppositely disposed valve seats 30a and 3la. Asshown, these seats are located so that the space 21a has a heightgreater than twice the thickness of the valve member 26a which makes itpossible for a part 31a, opening into said space at an intermediatepoint, to remain unobstructed whether the valve member 26a is in seatedposition on the seat 30a or on the seat 3ld. Moreover the seats 30a and3la are disposed intermediately of the valve casing so that a space 33ais provided below the valve seat 30a and a space 34a is provided abovethe valve seat 3la, each of said spaces 33a and 34a having a portopening therein as indicated at Ma and 360 respectively. The port 37aopening into aesauee the intermediate space 21a between the valve seats30a and tla communicates with the inlet port M of the compressionchamber H, for instance, by means of a conduit 38a, whereas the port 38aopening into the upper space 34a is connected directly with the suctionline 22, leading from the low temperature evaporator 5, and the port liaopening into the lower space 33a is connected indirectly with thesuction line 23 of the high temperature evaporator through a conduit 42aand a hermetrically sealed space 4311 defined by a housing a which, asin Fig. 1, may be the motor-compressor housing.

From the foregoing, it will be noted that when the valve member 26a isin lower position shown in full line, that is, when said member isseated on seat 30a, communication is established between the lowtemperature evaporator and the compression chamber II; but when thevalve member 280 is in upper position shown in broken line, that is whensaid member is seated on seat I 3la, communication is establishedbetween the high temperature evaporator 6 and said compression chamberii. Therefore, since the pressure in the high temperature evaporator 6is greater than the pressure in the low temperature evaporator 5, theeffective pressure on the underside of the valve member 26a is normallygreater than the effective pressure on the upper side of said member. Asin the embodiment shown in Fig. 1, these pressures are equalized orbalanced by means of supplemental pressure means 48a, such as a coilspring 49a which is arranged to act in the same manner. as hereinbeforedescribed in connection with spring 9 of the embodiment shown in saidFig. 1. Also as in that embodiment,

tion. Therefore the flow of refrigerant follows the course indicated bythe solid arrows, that is, gaseous refrigerant at the pressure existingin the low temperature evaporator 5 is admitted into the compressionchamber ll through the suction line 22, port a, valve casing spaces 34aand 21a, port 31a, conduit "a and intake port I4, and is compressed insaid chamber ii and discharged at condensing pressure through theexhaust port directly into the condenser ill, to be condensed thereinand delivered, in liquifled state, into the receiver tank l8 whenceliquid refrigerant may be supplied through liquid line i9 to theevaporators 5 and I in quantities controlled by the liquid iiowregulators and 2|. It will be understood that the pressure in the lowtemperature evaporator is thus reduced,

thereby tending to maintain the desired temperature-pressure value insaid evaporator.

If during operation of the system, the pressure in the high temperatureevaporator should rise to a point sufficient to cause the valve member26a to move to its upper position shown in broken lines, then the flowofrefrigerant follows the course indicated by the broken arrows, thatis, gaseous refrigerant at the pressure existing in the high pressureevaporator 6 is admitted into the compression chamber l i through thesuction line 23, hermetically sealed space 43a, conduit 42a, port a,valve casing spaces 33a and 21a, port 31a, conduit a. and intake portl4. The gaseous refrigerant thus admitted in the compressing chamber, iscompressed, condensed pressure resisting means 50a in the form of springpressed ball detents 5la, are provided to establish the predeterminedpressure differential at which the valve member 26a is to move from oneposition to another, said mechanisms being adapted to resist, withinselected limits, a change in the pressure value on either the lower orupper side of said valve member. .7

While the association of the spring pressed ball devices 5la. with thevalve member 26a as shown in Fig. 2, differs somewhat from theembodiment shown in Fig. 1, it will be noted that the action is the samein both instances. In Fig. 2, these devices are mounted for selectiveengagement either with a groove 52 or a groove 58 respectively disposedin spaced superimposed relation on a rod 54 suitably carried by thevalve member 26a for movement therewith. Thus, when valve member 2611 isin the lower position and the spring pressed balls engage the groove 52,the pressure on the underside of the valve member must reach a valuegreat enough to overcome the pressure on the upper side of said memberand the resistance imposed by said ball devices before the valve maymove to the upper position. Likewise, when valve member 26a is in thelower position and the spring pressed mechanisms engage the groove 53,the pressure on the upper side of the valve member must attain a valuesufflcient to overcome both the pressure on the underside of said memberand the resistance of the ball devices before the valve may move to thelower position.

The operation of they embodiment shown .in Fig. 2 may be summarized asfollows:

As shown, it is assumed that the system is operating on an on-cycle andthat the pressure in the low temperature evaporator 5 has caused thevalve member 28a to move to its lower posiand made available for theevaporators 5 and 6 in the same manner as above stated. The withdrawalof gaseous refrigerant from the high temperature evaporator 6 reducesits pressure thereby tending to maintain said evaporator at the desiredtemperature-pressure level.

From the foregoing it will be apparent that in the system shown in Fig.2, as in that appearing in Fig. 1, the valve member 26a is shifted backand forth from one position to the other in response to predetermineddepartures from an established balance in the pressure values onopposite sides of said member, and that such departures are a directresult of changes in the desired temperature-pressure levels in therespective low and high temperature evaporators. Accordingly, in thesystemshown in Fig. 2, as in the system shown in Fig. 1. neitherevaporator has actual preference over the other, but refrigeration willoccur alternately therein depending upon which evaporator demands themost refrigeration at any one moment during operation of the system. Inthis manner, each evaporator may be adequately maintained at itsrespective temperature level without detrimentally interferring with theoperation of the other. Al-

ample, there is shown in the drawings, a temperature type control deviceassociated with the low temperature evaporator 5, such device operatingfrom a thermostatic bulb 55 with a bellows or diaphragm 56 to actuate aswitch 51 for opening and closing an electric circuit 58 adapted tosupply current to the motor-compressor. Such a temperature controllingdevice, as well known in the art, will close the switch 51 thus startingthe motor-compressor when the temperature reaches a predetermined highlevel, and will open the switch thus stopping the motor-compressor whenthe temperature reaches a predetermined low level.

With particular reference to Fig. 2, a check valve 45a is preferablyprovided at the point of communication between the suction line 23 andthe hermetically sealed space 430., to prevent aseous refrigerant fromentering the low temperature evaporator 6, whenever the pressure in saidspace rises above the pressure in said evaporator.

Since in both embodiments of the invention shown in the drawings, thelow and high temperature evaporators are adapted to communicate with oneand the same compression chamber ll, it will be understood that themotor-compressor, at all times, will handle gas of a certain density andweight and. at other times, will handle gas of a different density andweight depending upon whether the compression chamber H is incommunication with the evaporator or the evaporator 6. In accordancewith the invention, provision is made for compensating this differencein gas density and weight so as to equalize the number of strokesrequired for and the amount of work performed in each phase ofoperation. As shown in the drawings, this is accomplished by providing aport 60 in the wall of the compressor cylinder I? at a pointintermediate the ends of the compression chamber ii to establish acommunicating connection between the compression chamber I l and thehermetically sealed space 43 (Fig. 1), or 43a (Fig. 2) the connectionincluding a casing iii, a tube 62, and a valve 63 which controls thepassage of gaseous refrigerant through said port into said space in themanner now to be described.

When gaseous refrigerant at the pressure existing in the low temperatureevaporator 5 is admitted into and compressed within the compressionchamber I l, the valve 63 remains closed because then the pressure insaid chamber is always lower than the pressure in the casing 6| which isin communication, through the tube 62, with the hermetically sealedspace wherein exists a pressure at least equal to the pressure of thehigh temperature evaporator 6. When gaseous refrigerant at the pressureexisting in the high temperature evaporator 6 is admitted into thecompression chamber H, the valve 63 still remains closed because thenthe pressure on both sides of this valve is equal, but the valve 63opens as the compression stroke of piston l3 begins due to the increasedpressure in said chamber. In this manner a portion of the heaviergaseous refrigerant admitted in the compression chamber ll may be bledback into the hermetically sealed space to be re-expanded therein.Movement of the piston over the part of the compression stroke whichremains after the port 60 is covered, effects normal compression of theheavier gas. By locating the port 60 so that a part-of the heaviergaseous refrigerant is bled away as described above, the weight of therefrigerant handled during compression of gaseous refrigerant fromeither the low or high. temperature evaporator may be substantiallybalanced and therefore, the work done per stroke and the number ofstrokes required for proper compression substantially equalized.

It will be understood that the invention is not 12 limited to thespecific embodiments herein shown and described, and that suchembodiments are subject to modification within the scope of the appendedclaims. I

I claim:

1. In a refrigerating system including a compressor, a condenser, a hightemperature evaporator, and a low temperature evaporator, anhermetically sealed chamber connected between the high temperatureevaporator and the compressor, a check valve permitting flow of fluidfrom the last-named evaporator to said chamber while preventing reverseflow, and valve means controlling the connection of the compressor withthe low temperature evaporator and with said chamber, said valve meansincluding an element adapted in one position to connect the said lowtemperature evaporator directly with the suction side of said compressorand in an alternative position to connect the suction side of thecompressor with said chamber, said valve means including also an elementadapted in alternative positions corresponding to the alternativepositions of the first-named element to connect the discharge side ofsaid compressor with the said chamber and with the condenserrespectively.

2. In two temperature refrigeration employing two evaporators operatedat difierent individual pressures from a common compression-condensersystem, the method which comprises connecting the evaporatorsindividually and alternately with the suction side of said compressor,diverting the liquid refrigerant discharge of the compressor from thecondenser to a pressure accumulator when one of said evaporators isconnected to the suction side of the compressor, directing therefrigerant discharge of the compressor to the condenser when the otherof said evaporators is connected to the suction side of the compressorand simultaneously connecting the accumulator chamber to the suctionside of the compressor to obtain a resultant second stage compression ofthe refrigerant.

3. In a refrigerating system including a compressor, a condenser, a hightemperature evaporator, and a low temperature evaporator, anhermetically sealed chamber connected between the high temperatureevaporator and the compressor, a check valve permitting flow of fluidfrom the high temperature evaporator to said chamber while preventingreverse flow, and valve means controlling the connection of thecompressor with the low temperature evaporator and with said chamber,said valve means including an element adapted in one position to connectthe last-named evaporator directly with the suction side of saidcompressor and in an alternative position to connect the suction side ofthe compressor with said chamber, said valve means including also anelement adapted in alternative positions corresponding to thealternative positions of the first-named element to connect thedischarge side of said compressor with the said chamber and with thecondenser respectively.

4. In a refrigerating system including a compressor, a condenser, a hightemperature evaporator, and a low temperature evaporator, anhermetically sealed chamber connected between the high temperatureevaporator and the compressor, and valve means controlling theconnection of the compressor with the low temperature evaporator andwith said chamber, said valve means including an element adapted in oneposition to connect the last-named evaporator directly with the suctionside of said compressor and in 13 v an alternative position toconnectthe suction side of the compressor with said chamber, said valvemeans including also an element adapted in alternative positionscorresponding to the alternative positions of the first-named element toconnect the discharge side of said compressor with the said chamber andwith the condenser respectively.

5. In a refrigerating system including a compressor, a condenser, a hightemperature evaporator, and a low temperature evaporator, a sealedchamber connected to the high temperature evaporator and to the suctionside of said compressor, a check valve permitting passage of fluid fromthe high temperature evaporator to the chamber and preventing flow inthe reverse direction, and valve means for controlling the connectionsbetween the compressor and the low temperature evaporator and betweenthe compressor and said chamber, said means including a pair of valveelements, one -of said valve elements being exposed at one side to thepressure in the low temperature evaporator and at the opposite side tothe pressure in said chamber so as to move under the influence of saidpressures into alternative positionsin one of which the said suctionside of the compressor is connected to the said low temperatureevaporator and in the other of which the suction side of the compressoris connected to the sealed chamber, the other valve element operating insynchronism with the valve element first named to connect the saidchamber directly with the discharge side of the compressor when the saidlow temperature evaporator is directly connected to the suction side ofthe compressor and for connecting the discharge side of the compressorwith the condenser when the said chamber is directly connected to thesuction side of said compressor.

6. A refrigerating system according to claim wherein pressure meansoperates on the first named valve element to augment the low tem-'perature evaporator pressure to which one side of the element issubjected whereby said element may be movable between the saidalternative positions in response to departures from a predeterminedpressure differential at the opposite sides of said element.

7. A refrigerating system according to claim 6 wherein means is providedfor preventing movement'of said first named valve. element until saiddeparture from the predetermined pressure difitfeigential has exceeded apredetermined magni- 8. A refrigerating system according to claim 5wherein the said sealedchamber takes the form. of a housing embracingthe compressor unit.

9. A refrigerating system according to claim 5 wherein means is providedfor bleeding a part of the refrigerant compressed in an individualcompression stroke of the compressor into the said 0 V a on Y Wtemperature evaporator, and a low temperature evaporator,said'evaporators being connected in parallel between the condenser andthe suction side of said compressor, a sealed chamber included in theconnection between the high temperature evaporator and the suction sideof the compressor, a check valve permitting flow from the hightemperature evaporator to the said chamber while sealed chamber, saidbleeding means being controlled by a check valve loaded to permit saidbleeding only when the pressure of the refrigerant in the compressor hasreached a predetermined preventing a reverse flow, and a valve deviceexposed to the pressures within the low temperature evaporator-andwithin said chamber and responsive to departures from a predetermineddifferential between said pressures for connecting said low temperatureevaporator and chamber individually and alternately to the suction sideof said compressor, said valve device including means for connecting thedischarge side of said compressor with the said chamber when the lowtemperature evaporator is connected to the suction side of thecompressor, and for connectingthe discharge side of the compressor withthe son'- denser when the said chamber is connected with the suctionside of said compressor. v

11. In a refrigerating system including a compressor having acompression chamber with suction and discharge ports, a condenserconnected to said discharge port, a high temperature evaporator, and alow temperature evaporator connected in parallel between the condenserand the suction port of said compressor, an accumulator chamber in theconnection between the high temperature evaporator and the compressorthrough which chamber the refrigerant flows in passing from the hightemperature evaporator to the said suction port, a check valvepermitting flow from the high temperature evaporator to the chamberwhile preventing reverse flow, valve means for connecting theaccumulator chamber and the low temperature evaporator individually andalternatively to the suction port of said compressor, and secondaryvalve means operative when the said low temperature evaporator isconnected to the suction port for diverting the refrigerant discharge ofsaid compressor to the accumulator chamber to the exclusion of flow ofsaid discharge to the condenser, and operative when the accumulatorchamber is connected to the said suction port for directing thedischarge of the compressor to the condenser. a

12. A refrigerating system according to claim 11 including meansoperative while the said accumulator chamber is connected with thesuction port of the compressor for bleeding a portion of the refrigerantfrom the said compression chamber back to the accumulator.

' EL'MER W. ZEARFOSS. J3.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATEiITB Number v Name Date 2,222,707 Fletcher NOV. 26,1940 2,440,534 Atkinson Apr. 2'1. 1948

